Absorption chiller and system incorporating the same

ABSTRACT

A device, such as an absorption chiller sub-system, is provided. The absorption chiller sub-system can include an evaporator and an absorber. The evaporator can be configured to receive a liquid first working fluid and to produce first working fluid vapor. The absorber can be configured to receive and combine first working fluid vapor and a second working fluid, for example, so as to release thermal energy. A divider having opposing first and second sides in respective fluid communication with the evaporator and the absorber can also be included. The divider can be configured to allow first working fluid vapor to pass therethrough between the first and second sides and to inhibit movement of liquid first working fluid therethrough between the first and second sides. Associated systems and methods are also provided.

BACKGROUND

Currently, there are approximately one million ground source geothermal(GSG) systems installed in the U.S., which GSG systems are utilized in arange of government, commercial, and residential contexts. Further,approximately 50,000 residential GSG systems are added each year. Theinstallation cost of GSG systems currently varies with geographicregion, but can be as much as $10,000 per ton capacity or more. And,while energy savings are expected with the use of GSG systems ascompared to more conventional heating and cooling systems, the paybackperiod for typical GSG systems is estimated to range from 5 to 10 years.It may therefore be desirable to develop a less complex and/or moreefficient GSG system, such that the cost of installation and/or thepayback period can be reduced.

BRIEF DESCRIPTION

In a first aspect, a device, such as an absorption chiller sub-system,is provided. The absorption chiller sub-system can include an evaporatorand an absorber. The evaporator can be configured to receive a liquidfirst working fluid and to produce first working fluid vapor. Theabsorber can be configured to receive and combine first working fluidvapor and a second working fluid, for example, so as to release thermalenergy.

A divider having opposing first and second sides in respective fluidcommunication with the evaporator and the absorber can also be included.For example, the evaporator and the absorber can be respectively coupledto the first side and second sides of the divider. The divider can beconfigured to allow first working fluid vapor to pass therethroughbetween the first and second sides and to inhibit movement of liquidfirst working fluid therethrough between the first and second sides. Forexample, the divider may define holes therethrough having diameters,say, less than or equal to about 100 nm. In some embodiments, thedivider can include a membrane.

The absorber can be configured to combine at least some first workingfluid vapor passing through the divider and a second working fluid so asto cause at least some first working fluid vapor passing through thedivider to become liquid. In some cases, the absorber can be configuredto receive the second working fluid such that an equilibrium secondpartial pressure of first working fluid vapor at the second side of thedivider is less than a first partial pressure of first working fluidvapor at the first side. For example, the evaporator can be configuredto receive liquid NH₃ as the liquid first working fluid, and theabsorber is configured to receive water or a mixture of water and NH₃ asthe second working fluid.

In some embodiments, the evaporator can be configured such that a totalpressure therein is at least twice a partial pressure of first workingfluid vapor at the first side of the divider. The absorber can beconfigured such that a total pressure therein is at least twice apartial pressure of first working fluid vapor at the second side of thedivider. Each of the evaporator and the absorber may be configured suchthat a respective total pressure therein is greater than or equal toabout atmospheric pressure.

The evaporator can be configured to receive liquid water and to producewater vapor, and the absorber can be configured to combine water vaporpassing through the divider and a relatively concentrated solutioncontaining lithium bromide so to produce a relatively diluted solutioncontaining lithium bromide. The divider can be formed at least partiallyof substantially hydrophobic material (e.g., polytetrafluoroethylene,polypropylene, or polyvinylidene fluoride) such that holes defined bythe divider are defined by the substantially hydrophobic material.

A generator may be included and configured to receive the relativelydiluted solution containing lithium bromide from the absorber and toproduce separate outputs of water vapor and the relatively concentratedsolution containing lithium bromide. A condenser can also be includedand configured to receive water vapor from the generator and to provideliquid water to the evaporator. The generator and condenser can be influid communication with opposing sides of a second divider that isconfigured to allow water vapor to pass therethrough and to inhibitmovement of liquid water therethrough, such that water vapor from thegenerator can pass through to the condenser while liquid water in thegenerator is substantially prevented from reaching the condenser.

A geothermal well, a heat exchanger, and a water heater can also beincluded. Each of the condenser, absorber, and evaporator can beconfigured to selectively thermally communicate with the geothermal welland the heat exchanger. In some embodiments, thermal energy may betransferred from the absorber and the condenser into a heated fluidstream, and thermal energy may be transferred from a cooled fluid streaminto the liquid first working fluid, with the heated fluid stream beingin selective fluid communication with each of the water heater, the heatexchanger, and the geothermal well, and the cooled fluid stream being inselective fluid communication with each of the heat exchanger and thegeothermal well. The geothermal well and the heat exchanger may also beconfigured to selectively exchange thermal energy directly therebetweenand to avoid exchanging thermal energy with each of the generator,condenser, evaporator, and absorber.

In another aspect, a method is provided, which includes providing adevice including an evaporator, an absorber, and a divider havingopposing first and second sides in fluid communication with theevaporator and the absorber, respectively. The divider can be configuredto allow first working fluid vapor to pass therethrough between thefirst and second sides and to inhibit movement of liquid first workingfluid therethrough between the first and second sides. Liquid firstworking fluid (e.g., liquid water) can be provided to the evaporator soas to produce first working fluid vapor (e.g., water vapor) thatcontacts the first side of the divider. First working fluid vaporpassing through the divider from the first side to the second side and asecond working fluid (e.g., a relatively concentrated solutioncontaining lithium bromide) can be received at the absorber, and atleast some first working fluid vapor passing through the divider can becombined in the absorber with the second working fluid, for example, soas to cause at least some of the first working fluid vapor passingthrough the divider to become liquid and/or release thermal energy (say,producing a relatively diluted solution containing lithium bromide).

In some embodiments, thermal energy can be supplied to the relativelydiluted solution containing lithium bromide so as to cause water toevaporate out and thereby produce the relatively concentrated solutioncontaining lithium bromide. Further, thermal energy can be removed fromthe water vapor produced from the relatively diluted solution containinglithium bromide so as to produce liquid water to be provided to theevaporator.

In some embodiments, the thermal energy removed from the water vaporproduced from the relatively diluted solution containing lithium bromidecan be selectively transferred to a heated fluid stream along withthermal energy from the absorber. Thermal energy can also be selectivelytransferred from a cooled fluid stream to the liquid water circulated tothe evaporator. Further, thermal energy can be selectively transferredbetween the heated fluid stream and at least one of a heat exchanger ora geothermal well, and also between the cooled fluid stream and at leastone of the heat exchanger and the geothermal well. In some cases, atarget temperature can be selected, and, when the target temperature ishigher than a ground temperature of the geothermal well, a geothermalfluid stream can be circulated between the geothermal well and the heatexchanger without receiving the thermal energy removed from the watervapor produced from the relatively diluted solution containing lithiumbromide and without exchanging thermal energy with the absorber.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a schematic view of an absorption chiller sub-systemconfigured in accordance with an example embodiment;

FIG. 2 is a cross sectional view of the absorption chiller sub-system ofFIG. 1;

FIG. 3 is a perspective exploded view of the absorption chillersub-system of FIG. 1;

FIG. 4 is a magnified view of the area labeled 4 in FIG. 2;

FIG. 5 is a magnified view of the area labeled 5 in FIG. 4;

FIG. 6 is a schematic side view of another example embodiment of theabsorption chiller sub-system of FIG. 1;

FIG. 7 is a magnified view of the area labeled 7 in FIG. 6;

FIG. 8 is a schematic view of the absorption chiller sub-system of FIG.1 in thermal communication with a source and a sink of thermal energy;

FIG. 9 is a schematic view of an absorption refrigeration systemconfigured in accordance with an example embodiment;

FIG. 10 is a schematic view of a heating and cooling system configuredin accordance with an example embodiment;

FIG. 11 is a schematic view of an absorption refrigeration systemconfigured in accordance with another example embodiment;

FIG. 12 is a schematic cross-sectional view of an absorption chillersystem configured in accordance with another example embodiment;

FIG. 13 is a magnified view of the area labeled 13 in FIG. 12;

FIG. 14 is a schematic cross-sectional view of an absorption chillersystem configured in accordance with yet another example embodiment;

FIG. 15 is a magnified view of the area labeled 15 in FIG. 14;

FIG. 16 is a schematic cross-sectional view of an absorption chillersystem configured in accordance with still another example embodiment;and

FIG. 17 is a magnified view of the area labeled 17 in FIG. 16.

DETAILED DESCRIPTION

Example embodiments of the present invention are described below indetail with reference to the accompanying drawings, where the samereference numerals denote the same parts throughout the drawings. Someof these embodiments may address the above and other needs.

Referring to FIGS. 1-4, therein is shown a device, such as an absorptionchiller sub-system 100, configured in accordance with an exampleembodiment. The absorption chiller sub-system 100 can include anevaporator 102 and an absorber 104. A divider, such as a membrane 106,can be disposed between the evaporator 102 and the absorber 104. Themembrane 106 can have opposing first and second sides 108, 110, with theevaporator 102 being in fluid communication with the first side and theabsorber 104 being in fluid communication with the second side. Forexample, in one embodiment, the evaporator 102 can be coupled to thefirst side 108 and the absorber 104 can be coupled to the second side110. In other embodiments, the evaporator 102 and absorber 104 may notbe directly coupled to the first and second sides 108, 110,respectively, but may still be configured to allow fluid to passthereto, for example, through an intermediate conduit.

The evaporator 102 can be configured to receive a liquid first workingfluid 112 a and to produce first working fluid vapor 112 b. For example,in one embodiment, the first working fluid 112 may be water, and theevaporator 102 may receive liquid water (for example, through a liquidinlet port 114) and may produce water vapor. Other candidate firstworking fluids are discussed below. Liquid first working fluid 112 a maycirculate through the evaporator 102, such that unevaporated portionsare outputted from the evaporator, say, at a liquid outlet port 116.

The absorber 104 can be configured to receive first working fluid vapor112 b and to combine at least some of that first working fluid vaporwith a second working fluid 118. The second working fluid 118 maycirculate through the absorber 104, such that the second working fluidis received, say, at an inlet port 120, travels through the absorber,and exits at an outlet port 122. Given that the second working fluid 118enters the absorber 104 and then is combined therein with first workingfluid vapor 112 b, the second working fluid 118 a entering the absorberhas a relatively lesser concentration therein of first working fluidthan does the second working fluid 118 b inside and exiting theabsorber. The second working fluid 118 a entering the absorber 104 atthe inlet port 120 is therefore referred to herein as “relativelyconcentrated second working fluid,” and the second working fluid 118 binside the absorber and exiting at the outlet port 122 is referred toherein as “relatively diluted second working fluid.”

The first and second working fluids 112, 118 may be chosen such that theact of combining first working fluid vapor 112 b and the second workingfluid causes a release of thermal energy. For example, the absorber 104can be configured to combine first working fluid vapor 112 b and thesecond working fluid 118 so as to cause at least some first workingfluid vapor 112 b to become liquid, thereby causing a release of thelatent heat of evaporation associated with the vapor. In someembodiments, the second working fluid 118 may include at least onecomponent (an “absorbent”) that tends to form a liquid solution with thefirst working fluid vapor 112 b, such that when the first working fluidvapor comes into contact with the second working fluid, the firstworking fluid vapor tends to transform into a liquid component of theliquid solution with the absorbent, thereby causing a release of theheat of absorption. In other embodiments, a chemical reaction may occurbetween the first working fluid vapor 112 b and a component of thesecond working fluid 118, which reaction may be exothermic and/or mayinduce a transformation of the first working fluid vapor 112 b to aliquid, thereby releasing heat of reaction and/or latent heat.

Referring to FIGS. 1-7, as mentioned, the membrane 106 can be disposedbetween, and in fluid communication with, the evaporator 102 and theabsorber 104. The first side 108 of the membrane 106 may therefore becontacted by liquid first working fluid 112 a and first working fluidvapor 112 b, and the second side 110 may be contacted by the secondworking fluid 118 and first working fluid vapor that may be disposed inthe absorber 104. In some embodiments, virtually all of the volumewithin the evaporator 102 may be occupied by liquid first working fluid112 a and/or all of the volume within the absorber 104 may be occupiedby the second working fluid 118 (as depicted in FIGS. 4 and 5). In suchcases, first working fluid vapor 112 b in the evaporator 102 would befound mainly at the first side 108 of the membrane 106, and firstworking fluid vapor 112 b in the absorber 104 would be found mainly atthe second side 110. In other embodiments (depicted by FIGS. 6 and 7),the volumes of the evaporator 102 and absorber 104 may be only partiallyoccupied by liquid first working fluid 112 a and (liquid) second workingfluid 118, such that first working fluid vapor 112 b may be found notonly at the first and second sides 108, 110, but throughout the volumesof the evaporator and absorber that are not otherwise occupied byliquids.

The membrane 106 may be configured to allow first working fluid vapor112 b to pass therethrough between the first and second sides 108, 110and to inhibit movement of liquid first working fluid 112 a, and thesecond working fluid 118, therethrough between said first and secondsides. For example, the membrane 106 may define holes 124 therethrough.The holes 124 may be sized in accordance with the properties of thefirst and second working fluids 112, 118 and those of the materialmaking up the membrane 106 in order to assure that the interfacialenergies of liquid first and second working fluids and the membrane aresuch that the liquid first and second working fluids are energeticallyprevented from assuming a configuration necessary to pass through theholes in the membrane. Further details regarding the sizing of the holes124, as well as the selection of the working fluids 112, 118 andmaterial for the membrane 106, are provided below. A general discussionof the use of porous membranes in fluid separation applications isprovided in Marcel Mulder, Basic Principles of Membrane Technology(Kluwer Academic Publishers, 1996), which is incorporated herein byreference in its entirety, and also in K. W. Lawson and D. R. Lloyd,“Review Membrane Distillation,” Journal of Membrane Science, 124 (1997),pp. 1-25, which is also incorporated herein by reference in itsentirety.

The second working fluid 118 can be chosen such that, when received atthe absorber 104 (under appropriate conditions), an equilibrium partialpressure P2 of first working fluid vapor 112 b at the second side 110(and possibly throughout the absorber) is less than a partial pressureP1 of first working fluid vapor at the first side 108 (and possiblythroughout the evaporator 102). For example, the first and secondworking fluids 112, 118 can be chosen such that the second working fluidincludes as a component thereof a liquid that has a strong affinity forthe first working fluid. In such a case, the equilibrium partialpressure P2 of the first working fluid vapor 112 b in the vicinity ofthe second working fluid 118 will tend to be low relative, say, to thepartial pressure P1 expected in the vicinity of liquid first workingfluid 112 a. Examples of pairs of first and second working fluids 112,118 that may be utilized in conjunction with embodiments of the abovedescribed absorption chiller sub-system 100 include, but are not limitedto, water and lithium bromide; NH₃ and water (or a mixture of water andNH₃); water and LiClO₃; water and CaCl₂, water and ZnCl₂; water andHnBr; water and H₂SO₄; and SO₂ and organic solvents.

The difference in partial pressures P1 and P2 of first working fluidvapor 112 b across the membrane 106 results in a driving force fordiffusion of first working fluid vapor from the first side 108 to thesecond side 110. Once first working fluid vapor 112 b reaches the secondside 110, it can be combined in the absorber 104 with the second workingfluid 118, with this combination being made more likely by the properchoice of a second working fluid having an affinity for first workingfluid. Mass (i.e., first working fluid 112) will therefore betransferred from the evaporator 102 to the absorber 104. In addition, asmass is transferred from the evaporator 102 to the absorber 104, thebalance in the evaporator between liquid first working fluid 112 a andfirst working fluid vapor 112 b will be disrupted, driving furtherevaporation of liquid first working fluid. It is noted that continuedevaporation of liquid first working fluid 112 a in the evaporator 102does not necessarily require the input of energy, but instead mayproceed simply due to the affinity of the second working fluid 118 forfirst working fluid.

As liquid first working fluid 112 a evaporates in the evaporator 102 toform first working fluid vapor 112 b, thermal energy is absorbed fromthe liquid first working fluid and used to overcome the latent heat ofevaporation of the first working fluid 112. As the first working fluidvapor 112 b moves through the membrane 106 and is combined in theabsorber 104 with the second working fluid 118 to form a liquid, thermalenergy in the form of latent heat of evaporation and/or absorption canbe released (as well as heat produced by any exothermic chemicalreactions that may take place between the first and second workingfluids). The overall result is a thermal energy transfer, associatedwith the mass transfer, from the liquid first working fluid 112 a in theevaporator 102 to the second working fluid 118 in the absorber 104. Themembrane 106 can be configured such that the surface area presented tothe first working fluid 112 at the first side 108 and to the secondworking fluid 118 at the second side 110 is sufficient to facilitate adesired level of thermal energy transfer.

With the evaporator 102 and the absorber 104 separated by the membrane106 as discussed above, it may not be required that the total pressurewithin either of the evaporator or the absorber is approximately thesame as the respective partial pressure therein of first working fluidvapor 112 b, as may have been the case for previous absorption chillersub-systems. Rather, the evaporator 102 may be configured such that thetotal pressure therein is at least twice the partial pressure P1 offirst working fluid vapor 112 b. Further, the absorber 104 may beconfigured such that the total pressure therein is at least twice thepartial pressure P2 of first working fluid vapor 112 b. As such,embodiments of the absorption chiller sub-system 100 may have a totalsize and weight that is significantly reduced with respect to previousabsorption chiller sub-systems.

For the first working fluid vapor 112 b to be driven from one side ofthe membrane 106 to the other, particular temperatures and pressures areneeded. As mentioned above, the evaporation of liquid first workingfluid 112 a in the evaporator 102, the diffusion of first working fluidvapor 112 b from the first side 108 of the membrane 106 to the secondside 110, and the absorption of first working fluid vapor (or otherenergy-releasing event) in the absorber 104 can proceed spontaneously,acting to transfer thermal energy from the evaporator to the absorber.However, as thermal energy is transferred, the temperature of the liquidfirst working fluid 112 a (in the absence of any other energy transfers)will drop, thereby reducing (and eventually eliminating) the tendencyfor further evaporation. At the same time, the temperature of the secondworking fluid 118 (again, in the absence of any other energy transfers)will rise, thereby decreasing (and eventually eliminating) the tendencyof first working fluid vapor 112 b therein to be absorbed. It is notedthat, in some embodiments, the membrane 106 may include a thermallyinsulating material, thereby preventing the transfer of heattherethrough from the absorber 104 to the evaporator 102.

Referring to FIG. 8, in order to allow the transfer of thermal energyfrom the evaporator 102 to the absorber 104 to continue, the evaporatorcan be brought into thermal contact with a thermal energy source 126,while the absorber can be brought into thermal contact with a thermalenergy sink 128. For example, a cooled fluid stream 130 (e.g., air orwater) can be circulated between the thermal energy source 126 and theevaporator 102 by a pump 132, and a heated fluid stream 134 (e.g., airor water) can be circulated between the absorber 104 and the thermalenergy sink 128 by a pump 136. The absorption chiller sub-system 100 cantherefore be used to extract thermal energy from the thermal energysource 126 and to deposit thermal energy at a thermal energy sink 128.In some embodiments, the temperature T_(source) at the thermal energysource 126 may be lower than the temperature T_(sink) at the thermalenergy sink 128, in which case the absorption chiller sub-system 100operates as a heat pump. Any barriers separating the first working fluid112 a in the evaporator 102 and the cooled fluid stream 130 (e.g., anouter wall defining the evaporator), and/or any barriers separating thesecond working fluid 118 a in the absorber 104 and the heated fluidstream 134 (e.g., an outer wall defining the absorber), can beconfigured to have a relatively low thermal resistance, therebyfacilitating thermal energy transfer thereacross.

Referring to FIG. 9, therein is shown an absorption refrigeration system140 (also referred to as an absorption chiller system) that incorporatesthe absorption chiller sub-system 100. A generator 142 may receive therelatively diluted second working fluid 118 b that is outputted at theoutlet port 122 of the absorber 104. As mentioned above, the secondworking fluid 118 b that is outputted from the absorber 104 has beencombined therein with first working fluid vapor 112 b passing throughthe membrane 106. A pump 144 can be used to urge the relatively dilutedsecond working fluid 118 b towards the generator 142. The generator 142can be configured to receive the relatively diluted second working fluid118 b and to produce separate outputs of first working fluid vapor 112 band a relatively concentrated second working fluid 118 a. For example,thermal energy 146 can be added at the generator 142 in order to raisethe temperature of the relatively diluted second working fluid 118 b,thereby driving some of the first working fluid dissolved therein out ofthe solution as first working fluid vapor 112 b. The remaining secondworking fluid, now being relatively concentrated second working fluid118 a, can be directed back to the inlet port 120 of the absorber 104.

The first working fluid vapor 112 b outputted from the generator 142 canbe directed to a condenser 148. The condenser 148 can receive the firstworking fluid vapor 112 b and to provide liquid first working fluid 112a to the evaporator 102. For example, thermal energy 150 can be removedat the condenser 148, say, through the use of a heat exchanger, in orderto cause the first working fluid vapor 112 b to condense.

Overall, the evaporator 102, absorber 104, generator 142, and condenser148 may operate so as to form a continuous cycle in which the secondworking fluid 118 is combined with first working fluid 112 at theabsorber and separated from first working fluid at the generator, andfirst working fluid is converted from gas to liquid at the condenser andfrom liquid to gas at the evaporator. The system 140 acts to affect thetransfer of thermal energy from a source 126 to a sink 128. The onlyinput of energy that may be required to sustain the operation of thesystem 140 is the thermal energy 146 that is directed to the generator142 (and a small amount of energy required to circulate the secondworking fluid 118, for example, through the operation of the pump 144),which thermal energy may be supplied by, for example, the exhaust of aninternal combustion engine, engine fluid such as water/glycol or oil, aburner, a solar collector, and/or the exhaust of a gas turbine.

Referring to FIG. 10, therein is shown a heating and cooling system 260configured in accordance with an example embodiment. The heating andcooling system 260 can include an absorption refrigeration system 240that incorporates an absorption chiller sub-system 200 as describedabove with an evaporator 202 and an absorber 204 separated by a membrane206. The absorption chiller sub-system 200 can employ water as the firstworking fluid 212, such that the evaporator 202 is configured to receiveliquid water 212 a and to produce water vapor 212 b.

The membrane 206 can define holes 224 that extend between the evaporator202 and the absorber 204. The membrane 206, or at least the portionsthrough which the holes 224 are defined, may be formed of substantiallyhydrophobic material (e.g., polytetrafluoroethylene, polypropylene,and/or polyvinylidene fluoride). By forming the holes 224 with a maximumdiameter of about 100 nm from a substantially hydrophobic material, themovement of liquid water 212 a through the membrane 206 is substantiallyprevented, due to the surface energy effects discussed above, whilewater vapor 212 b is permitted to pass through the holes between theevaporator 202 and absorber 204. As mentioned earlier, in someembodiments, the membrane 206 may be formed of thermally insulatingmaterial, with examples being the hydrophobic materials listed above.

The absorption chiller sub-system 200 can also employ a solution oflithium bromide and water 218 as the second working fluid. The absorber204 can be configured to combine water vapor 212 b passing through themembrane 206 with the lithium bromide-water solution 218 a entering atan inlet port 220, thereby forming in the absorber a lithiumbromide-water solution 218 b that is relatively diluted with respect tolithium bromide content (the solution previously being relativelyconcentrated with respect to lithium bromide content prior to beingcombined with water vapor passing through the membrane 206). Lithiumbromide tends to have a strong affinity for water, such that the partialpressure of water vapor in the vicinity of lithium bromide tends to berelatively low and the diffusion of water vapor through the membrane 206is facilitated.

As mentioned above, the use of a membrane 206 between the evaporator 202and absorber 204 may alleviate the need to maintain the total pressurein either of the evaporator or the absorber at a level that is aboutequal to the partial pressure of water vapor in either one.Specifically, each of the evaporator 202 and the absorber 204 may beconfigured such that a respective total pressure therein is greater thanor equal to about atmospheric pressure. This may reduce the size, cost,and/or complexity of the evaporator 202 and absorber 204. In otherembodiments either the evaporator 202 or the absorber 204 may beconfigured to operate either above or below atmospheric pressure.

The absorption refrigeration system 240 can also include a generator242, which can receive the relatively diluted lithium bromide-watersolution 218 b from the absorber 204 (e.g., the relatively dilutedlithium bromide-water solution exiting the absorber at the outlet port222) and thermal energy 246 from an external source (not shown) to heatthe diluted lithium bromide-water solution so as to produce separateoutputs of water vapor 212 b and the relatively concentrated containinglithium bromide-water solution 218 a that is ultimately received at theinlet port 220. The lithium bromide-water solution 218 can be circulatedbetween the absorber 204 and the generator 242, say, through the use ofa pump 244.

As the absorption refrigeration system 240 operates, thermal energy canbe transferred from the evaporator 202 to the absorber 204. The thermalenergy deposited at the absorber 204 can then be rejected, say, to theambient environment or some other energy sink. A cooled water stream 230can be disposed in thermal contact with the evaporator 202, and thermalenergy can be transferred from the cooled water stream to the evaporator(e.g., to the water 212 a therein), thereby affecting (in the absence ofother thermal transfers) a temperature decrease in the cooled waterstream.

The water vapor 212 b outputted by the generator 242 can be directed toa condenser 248, at which thermal energy can be removed from the watervapor in order to produce liquid water 212 a. The liquid water 212 b canthen be directed to the evaporator 202 to repeat the cycle. A heatedwater stream 262 can be disposed in thermal contact with the condenser248 such that the thermal energy extracted from the water vapor 212 b istransferred (at least in part) to the heated water stream, therebyaffecting (in the absence of other thermal transfers) a temperatureincrease in the heated water stream.

The heated water stream 262 can be circulated to each of a geothermalwell 264, a water heater 266, and a heat exchanger 268 (the last ofwhich may be used, for example, as a space heater/cooler) via manifolds270. Thermal energy in the heated water stream 262 (received, forexample, at the condenser 248) can then used to produce heat and hotwater for residential or commercial use via the heat exchanger 268 andwater heater 266, respectively, and/or can be rejected at the geothermalwell 264. The heated water stream 262 can be connected to the geothermalwell 264 and the heat exchanger 268 with valves 272 that allow theheated water stream to be selectively directed to or away from each ofthe geothermal well and the heat exchanger. In this way, heat can beprovided via the heat exchanger only when desired (e.g., in the winter).In some embodiments, the heated water stream 262 may also be disposed inthermal communication with the absorber 204, such that thermal energyrejected at the absorber may be used to heat the heated water stream.

The cooled water stream 230 can be circulated to each of the geothermalwell 264 and a heat exchanger 268 (the last of which may be used, forexample, as a space heater/cooler) via manifolds 274. Thermal energy canthen be transferred to the cooled water stream 230 at the heat exchanger268 in order to provide ambient cooling or at the geothermal well 264(with the thermal energy ultimately being rejected, for example, at theevaporator 202). The cooled water stream 230 can be connected to thegeothermal well 264 and the heat exchanger 268 with valves 272 thatallow the cooled water stream to be selectively directed to or away fromeach of the geothermal well and the heat exchanger. In this way, coolingcan be provided via the heat exchanger only when desired (e.g., in thesummer).

Valves 276 may be included that function so as to selectively create ageothermal fluid circulation loop 278 that allows fluid (a “geothermalfluid stream”) to circulate directly between the geothermal well 264 andthe heat exchanger 268, this loop being otherwise isolated from theabsorption refrigeration system 240. When the valves 276 are sopositioned to isolate the fluid circulation loop 278 from the absorptionrefrigeration system 240, the geothermal well 264 and heat exchanger 268may exchange thermal energy directly therebetween (via the geothermalfluid stream in the geothermal fluid circulation loop) withoutexchanging thermal energy with any of the generator 242, condenser 248,evaporator 202, and/or absorber 204.

The valves 276 may allow the heating and cooling system 260 to beoperated more efficiently, under certain conditions, by foregoing theuse of the absorption refrigeration system 240, the use of whichrequires some energy input at the generator 242. For example,considering the use of the heat exchanger 268 as a residential airconditioning unit for cooling a home, during summer months, thetemperature of the ground surrounding the geothermal well 264 may belower than a desired air temperature (a “target” temperature) for thehome. In that case, the valves 276 can be adjusted to cause thegeothermal fluid stream to circulate (say, with the help of a pump 279)directly between the geothermal well 264 and the heat exchanger 268,without interacting with the absorption refrigeration system 240. Atthese times, operation of the absorption refrigeration system 240 can beceased entirely, avoiding the expenditure of energy otherwise requiredto operate that system. The heating and cooling system 260 can beconfigured to automatically switch between this “direct geothermal mode”of operation and the absorption refrigeration mode of operation inresponse to the ground temperature of the geothermal well 264 and auser-selected target temperature.

Referring to FIG. 11, therein is shown an absorption refrigerationsystem 340 configured in accordance with another example embodiment. Aswith the embodiment depicted in FIG. 9 and described above, theabsorption refrigeration system 340 includes an absorption chillersub-system 300. The absorption chiller sub-system 300 has an evaporator302 and an absorber 304 separated by a first divider, such as a firstmembrane 306 a, that is configured, for selected working fluids(including a first working fluid), to allow vapor to pass therethroughand to substantially prevent the passage of liquid. Liquid first workingfluid 312 a can be received by the evaporator 302 so as to produce firstworking fluid vapor 312 b that passes through the first membrane 306 aand to the absorber 304, where it is combined with relativelyconcentrated second working fluid 318 a in order to produce relativelydiluted second working fluid 318 b. As mentioned earlier, this processcan result in the transfer of thermal energy 380 into the evaporator 302and across the first membrane 306 a and into the absorber 304, withthermal energy 382 ultimately being rejected at the absorber.

The absorption refrigeration system 340 can also include a generator 342and a condenser 348 each in fluid communication with opposing sides of asecond membrane 306 b. The second membrane 306 b, like the firstmembrane 306 a, can be configured to allow first working fluid vapor topass therethrough and to inhibit movement of liquid first working fluidtherethrough. The generator 342 can receive the relatively dilutedsecond working fluid 318 b being outputted from the absorber 304.Thermal energy 346 can be provided to the relatively diluted secondworking fluid 318 b so as to cause first working fluid vapor 312 b to bereleased from the second working fluid, thereby producing relativelyconcentrated second working fluid 318 a that can be directed to theabsorber 304. The first working fluid vapor 312 b released from thesecond working fluid 318 can then pass through the second membrane 306 bto the condenser 348, where thermal energy 350 can be removed totransform the vapor to liquid first working fluid 312 a.

Referring to FIGS. 12 and 13, therein is shown an absorption chillersub-system 400 configured in accordance with another example embodiment.The absorption chiller sub-system 400 can include an evaporator 402 andan absorber 404. A membrane 406 can be disposed between the evaporator402 and the absorber 404. The membrane 406 can have opposing first andsecond sides 408, 410, and second working fluid 418 in the absorber 404can be in direct contact with the second side. A barrier 490 can beincluded between the evaporator 402 and the membrane 406, beingseparated from the membrane by spacers 492. The barrier 490 can beconfigured such that liquid first working fluid 412 a in the evaporator402 is substantially prevented from contacting the first side 408 of themembrane, while first working fluid vapor 412 b is allowed to passthrough the barrier to the membrane and, ultimately, the absorber 404.The barrier 490 therefore results in the establishment of a vapor gap494 between liquid first working fluid 412 a in the evaporator 402 andthe membrane 406.

The barrier 490 can be a relatively simple structure, such as a mesh,that is relatively permeable to liquids. Penetration of liquid firstworking fluid 412 a from the evaporator 402 through the barrier 490 canbe substantially prevented by configuring the absorption chillersub-system 400 such that the liquid first working fluid entering theevaporator at the inlet port 414 has a relatively low hydrostaticpressure and a velocity V directed substantially parallel to thebarrier. In this way, the liquid first working fluid 412 a in theevaporator 402 would be expected to have a small (nearly zero) velocitycomponent directed toward the barrier 490.

The vapor gap 494 may affect a decrease in the rate at which thermalenergy is transmitted from the (potentially hotter) absorber 404 to the(potentially colder) evaporator 402. Conduction across the vapor gap 494will be substantially limited to the energy transferred betweencolliding gaseous molecules, which process is expected to besubstantially less efficient than conduction through a solid body. Thevapor gap 494 may also result in a reduction in the mass transfer ratebetween the evaporator 402 and the absorber 404, causing a correspondingloss in thermal transfer efficiency from the evaporator to the absorber.

Referring to FIGS. 14 and 15, in another embodiment, a vapor gap can beestablished on the absorber side of the membrane rather than on theevaporator side, as in the previous embodiment. That is, an absorptionchiller sub-system 500 can include a membrane 506 can have opposingfirst and second sides 508, 510, with liquid first working fluid 512 ain the evaporator 502 being in direct contact with the first side. Abarrier 590 can be included between the absorber 504 and the membrane506, being separated from the membrane by spacers 592. The barrier 590can be configured such that second working fluid 518 in the absorber issubstantially prevented from passing through the barrier, while firstworking fluid vapor 412 b is allowed to pass through the barrier to theabsorber 404. The barrier 590 therefore results in the establishment ofa vapor gap 594 between the membrane 506 and second working fluid 518 inthe absorber 504.

As mentioned above, in order to assure that the liquid does notpenetrate the barrier 490, 590, the hydrostatic pressure of the fluidcontacting the barrier should be relatively small. Referring to FIGS. 16and 17, in another embodiment, an absorption chiller sub-system 600 caninclude an evaporator 602 and an absorber 604 separated by a pair ofmembranes 606 a, 606 b. The membranes 606 a, 606 b can be configured asdiscussed earlier so as to allow passage therethrough of first workingfluid vapor 612 b but not liquid first or second working fluids 612 a,618. The pair of membranes 606 a, 606 b (which may be integrated into aunitary structure) can be separated by a vapor gap 694, thereby limitingthermal conduction across the membranes from the absorber 604 to theevaporator 602. In some embodiments, the hydrostatic pressure of eitherof liquid first working fluid 612 a in the evaporator 602 or secondworking fluid 618 in the absorber 604 can be relatively high, whichaspect may simplify the overall design of the absorption chillersub-system 600.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. For example, while absorption refrigeration systemshave been described that incorporate an evaporator and absorber coupledacross a porous membrane and utilized in conjunction with either aconventional generator and condenser or a generator-condensercombination in which the generator and condenser are coupled across aporous membrane, it is also possible to utilize agenerator-membrane-condenser combination with a conventional evaporatorand absorber. Finally, while single stage or “single effect” absorptionrefrigeration systems have been described above, the concepts disclosedherein are also amenable to use in “multiple effect” or cascadedsystems, in which the thermal energy that is outputted from one thermalcycling system (say, at the absorber and/or condenser) acts as thedriving force for another thermal cycle (say, being the input to thegenerator). It is, therefore, to be understood that the appended claimsare intended to cover all such modifications and changes as fall withinthe true spirit of the invention.

1. A device comprising: an evaporator configured to receive a liquidfirst working fluid and to produce first working fluid vapor; anabsorber configured to receive and combine first working fluid vapor anda second working fluid a divider having opposing first and second sidesin respective fluid communication with said evaporator and saidabsorber, said divider being configured to allow first working fluidvapor to pass therethrough between said first and second sides and toinhibit movement of liquid first working fluid therethrough between saidfirst and second sides.
 2. The device of claim 1, wherein saidevaporator is coupled to said first side of said divider and saidabsorber is coupled to said second side of said divider.
 3. The deviceof claim 1, wherein said absorber is configured to combine at least somefirst working fluid vapor passing through said divider and a secondworking fluid so as to cause at least some first working fluid vaporpassing through said divider to become liquid.
 4. The device of claim 1,wherein said divider includes a membrane.
 5. The device of claim 1,wherein said divider defines holes therethrough.
 6. The device of claim1, wherein said absorber is configured to combine at least some firstworking fluid vapor passing through said divider and a second workingfluid so as to release thermal energy.
 7. The device of claim 1, whereinsaid absorber is configured to receive a second working fluid such thatan equilibrium second partial pressure of first working fluid vapor atsaid second side is less than a first partial pressure of first workingfluid vapor at said first side.
 8. The device of claim 1, wherein saidevaporator is configured to receive liquid NH₃ as the liquid firstworking fluid.
 9. The device of claim 8, wherein said absorber isconfigured to receive at least one of water or a mixture of water andNH₃ as the second working fluid.
 10. The device of claim 1, wherein saidevaporator is configured such that a total pressure therein is at leasttwice a partial pressure of first working fluid vapor at said firstside.
 11. The device of claim 10, wherein said absorber is configuredsuch that a total pressure therein is at least twice a partial pressureof first working fluid vapor at said second side.
 12. The device ofclaim 1, wherein said evaporator is configured to receive liquid waterand to produce water vapor, and said absorber is configured to combinewater vapor passing through said divider and a relatively concentratedsolution containing lithium bromide so to produce a relatively dilutedsolution containing lithium bromide.
 13. The device of claim 12, whereineach of said evaporator and said absorber is configured such that arespective total pressure therein is greater than or equal to aboutatmospheric pressure.
 14. The device of claim 12, wherein said dividerdefines holes therethrough having diameters less than or equal to about100 nm.
 15. The device of claim 12, wherein said divider is formed atleast partially of substantially hydrophobic material such that holesdefined by said divider are defined by said substantially hydrophobicmaterial.
 16. The device of claim 15, wherein said substantiallyhydrophobic material includes at least one of polytetrafluoroethylene,polypropylene, or polyvinylidene fluoride.
 17. The device of claim 12,further comprising: a generator configured to receive the relativelydiluted solution containing lithium bromide from said absorber and toproduce separate outputs of water vapor and the relatively concentratedsolution containing lithium bromide; and a condenser configured toreceive water vapor from said generator and to provide liquid water tosaid evaporator.
 18. The device of claim 17, further comprising a seconddivider configured to allow water vapor to pass therethrough and toinhibit movement of liquid water therethrough, wherein said generatorand said condenser are in fluid communication with opposing sides ofsaid second divider such that water vapor from said generator can passthrough said second divider to said condenser while liquid water in saidgenerator is substantially prevented from reaching said condenser. 19.The device of claim 17, further comprising: a geothermal well; and aheat exchanger, wherein each of said condenser, absorber, and evaporatorare configured to selectively thermally communicate with said geothermalwell and said heat exchanger.
 20. The device of claim 19, furthercomprising a water heater, wherein said device is configured such thatthermal energy is transferred from said absorber and said condenser intoa heated fluid stream, and thermal energy is transferred from a cooledfluid stream into the liquid first working fluid, the heated fluidstream being in selective fluid communication with each of said waterheater, said heat exchanger, and said geothermal well, and the cooledfluid stream being in selective fluid communication with each of saidheat exchanger and said geothermal well.
 21. The device of claim 19,wherein said geothermal well and said heat exchanger are configured toselectively exchange thermal energy directly therebetween and to avoidexchanging thermal energy with each of said generator, condenser,evaporator, and absorber.
 22. A method comprising: providing a deviceincluding an evaporator, an absorber, and a divider having opposingfirst and second sides in fluid communication with the evaporator andthe absorber, respectively, and configured to allow first working fluidvapor to pass therethrough between the first and second sides and toinhibit movement of liquid first working fluid therethrough between thefirst and second sides; providing liquid first working fluid to theevaporator so as to produce first working fluid vapor that contacts thefirst side of the divider; receiving at the absorber first working fluidvapor passing through the divider from the first side to the second sideand a second working fluid; and combining in the absorber at least somefirst working fluid vapor passing through the divider and the secondworking fluid.
 23. The method of claim 22, wherein said combining atleast some first working fluid vapor passing through the divider and thesecond working fluid includes combining at least some first workingfluid vapor passing through the divider and the second working fluid soas to cause at least some of the first working fluid vapor passingthrough the divider to become liquid.
 24. The method of claim 22,wherein said combining at least some first working fluid vapor passingthrough the divider and the second working fluid includes combining atleast some first working fluid vapor passing through the divider and thesecond working fluid so as to release thermal energy.
 25. The method ofclaim 22, wherein said providing a liquid first working fluid to theevaporator includes providing liquid water to the evaporator so as toproduce water vapor, and said combining in the absorber at least somefirst working fluid vapor and the second working fluid includescombining at least some water vapor and a relatively concentratedsolution containing lithium bromide.
 26. The method of claim 25, whereinsaid providing liquid water to the evaporator so as to produce watervapor includes providing liquid water to the evaporator so as to producewater vapor with a first partial pressure at the first side, and saidreceiving at the absorber a relatively concentrated solution containinglithium bromide includes receiving at the absorber a relativelyconcentrated solution containing lithium bromide such that anequilibrium second partial pressure of water vapor at the second side isless than the first partial pressure at the first side.
 27. The methodof claim 25, wherein said providing a device includes providing a devicethat includes a divider formed at least partially of substantiallyhydrophobic material and defining holes therethrough, the holes havingdiameters less than or equal to about 100 nm.
 28. The method of claim25, further comprising supplying thermal energy to a relatively dilutedsolution containing lithium bromide so as to cause water to evaporateout and thereby produce the relatively concentrated solution containinglithium bromide; and removing thermal energy from the water vaporproduced from the relatively diluted solution containing lithium bromideso as to produce liquid water to be provided to the evaporator.
 29. Themethod of claim 28, further comprising: selectively transferring thethermal energy removed from the water vapor produced from the relativelydiluted solution containing lithium bromide and transferring thermalenergy from the absorber to a heated fluid stream; selectivelytransferring thermal energy from a cooled fluid stream to the liquidwater circulated to the evaporator; selectively transferring thermalenergy between the heated fluid stream and at least one of a heatexchanger or a geothermal well; and selectively transferring thermalenergy between the cooled fluid stream and at least one of the heatexchanger and the geothermal well.
 30. The method of claim 29, furthercomprising: selecting a target temperature; and causing, when the targettemperature is higher than a ground temperature of the geothermal well,a geothermal fluid stream to circulate between the geothermal well andthe heat exchanger without receiving the thermal energy removed from thewater vapor produced from the relatively diluted solution containinglithium bromide and without exchanging thermal energy with the absorber.31. A device comprising: a first working fluid; a second working fluid;a divider having opposing first and second sides in respective fluidcommunication with said evaporator and said absorber, said divider beingconfigured such that first working fluid vapor passes therethrough whilemovement of liquid first working fluid therethrough is inhibited; anevaporator in fluid communication with said first side, said evaporatorreceiving said first working fluid as liquid first working fluid andproducing first working fluid vapor with a first partial pressure atsaid first side; and an absorber that receives said second working fluidunder conditions such that an equilibrium second partial pressure offirst working fluid vapor at said second side is less than the firstpartial pressure, such that said first working fluid vapor moves fromsaid first side to said second side and is combined with said secondworking fluid in said absorber.
 32. The device of claim 31, wherein saidsecond working fluid is received in said absorber as liquid secondworking fluid and combined with first working fluid vapor passingthrough said divider so as to cause at least some of said first workingfluid vapor passing through said divider to become liquid.
 33. Thedevice of claim 31, wherein a total pressure in said evaporator is atleast twice the first partial pressure.